The present invention relates to a spinning preparation machine as well as to a process for the calibration of a spinning preparation machine.
In the spinning industry, first a homogenized fiber sliver and finally, as an end product, a twisted yarn is produced in several process steps, e.g., from cotton. The spinning preparation machines upstream of the yarn production, such as cards, combing machines and drawing frames have in particular the task to even out the sliver mass fluctuations of one or several fiber slivers. For this purpose, sliver sensors are installed, e.g., on draw frames, and these measure the sliver thickness or sliver mass or their fluctuations, and transmit this information to an autoleveling unit that actuates at least one of the drafting elements of the drawing frame as required. One example of a draw frame operating according to such a regulating principle is model RSB-D30 of the RIETER Company. Even with drawing frame not equipped with autoleveling, information concerning the fluctuation of sliver thickness is desired in many instances. A suitable sensor at the output of such drawing frames emits a suitable switch-off signal for the machine and/or a warning signal, if a threshold value of the sliver mass or the sliver thickness is not reached or exceeded.
To measure the fluctuation of sliver thickness, mechanical scanning devices are known, and these are used today in almost all machines of this type. However, the dynamics of these mechanical sensors are no longer sufficient with output speeds of more than 1000 m/min and a high requirement profile. Furthermore, the strong mechanical compression that is necessary before the mechanical sensor has a negative effect on the drafting ability.
In addition to mechanical scanning of the fluctuation of sliver thickness, other scanning principles have been proposed. Thus, e.g., it is known from U.S. Pat. No. 2,942,303 and DE 44 45 720 A1 that the sliver thickness can be measured without contact, by means of penetrating optical radiation. The measuring precision is however strongly subject to environmental influences in that case, e.g., temperature, humidity and pollution.
Furthermore, the process is susceptible to color as well as to reflection characteristics of the fiber sliver.
With other known measuring techniques, contact-less measuring methods use ultrasound waves. Capacitive or pneumatic measuring methods are also known. It has also been proposed to use X-rays or gamma rays. However, all of these processes are sensitive to humidity. Therefore, it does not help much that climatic influences such as temperature and relative air humidity can be compensated for as a rule, so that climatic influences can be minimized. The problem of inherent fiber moisture cannot be easily removed thereby. In addition, the fiber moisture can vary by up to 5% in one and the same batch of cotton at constant environmental conditions. Also, the upper layers of cotton in a can presented to a spinning preparation machine absorb more moisture than the lower ones. Furthermore, the moisture of the textile fibers varies due to changes in climatic conditions in the spinning mill—e.g., moisture varies from the morning as compared to noon and night. The above-mentioned influences in turn exercise a great influence on the measuring results of sliver thickness, and thereby on the quality of regulating. Overall, these processes are therefore hardly suitable for high-precision measuring of the fiber sliver thickness.
A relatively new method to measure the sliver thickness is based on the utilization of microwaves. WO 00/12974 describes such a measuring system using microwaves, according to which microwaves were coupled to a resonator through which one or several fiber slivers are conveyed. The attenuation and the resonance frequency shift is then measured based on the presence of the fiber sliver or slivers, and the fluctuations of thickness and possibly the moisture content of the fiber sliver or slivers are derived from the measured values. EP 0 468 023 B1 describes a similar microwave measuring method that can be transferred to the measuring of fiber sliver. The sensors based on microwave resonator technology offer in particular the advantage that the environmental conditions, such as e.g. room temperature and room humidity, are already taken into account so that they need not be compensated for any further.
However, the sensors as well as the corresponding measuring methods described and shown in the above-mentioned publications are still underdeveloped in many aspects and in need of improvement. The specific adaptation to the problems of measuring fiber slivers in particular requires new solutions.